Flame and smoke retardant materials generally fall into two categories, halogenated retardants and non-halogenated retardants. Retardants, as used unmodified herein, refers to both flame and smoke retardants. Non-halogenated systems, such as magnesium hydroxide, aluminum trihydrate, ammonium phosphate, etc. generally require loadings of up to 60% of flame retardant in the resinous compound. This is due to the mechanism by which the retardant works. For instance, aluminum trihydrate operates by releasing water upon heating. The dehydration reaction is endothermic and absorbs some of the heat of reaction of the resinous compound.
In resinous fiber production, loadings above 8% retardant are generally not considered acceptable. This is especially true with respect to fine denier (very small diameter) fibers. Lower loadings may be achieved by the use of halogenated systems. See, for example, U.S. Pat. No. 4,006,118 showing a brominated alkoxydiphenyl sulfone derivative useful as an additive in thermoplastic polymer compositions, to act as a flame retardant.
However, even most halogenated retardant compounds cannot achieve acceptable flame and smoke retardancy with such small load levels. Thus, manufacturers have turned to the use of hybrid retardants comprising both non-halogenated and halogenated systems. The two systems seem to have a synergistic effect and can be used together at lower load levels to achieve better flame and smoke retardancy than either compound alone could achieve.
Antimony trioxide (Sb.sub.2 O.sub.3) is one non-halogenated compound which has been used as a flame retardant additive in conjunction with halogenated retardant compounds. Antimony trioxide is a particulate compound and is mixed with the base compound and the halogenated retardant compound to form a flame retardant system.
Heretofore however, the addition of particulate retardants such as antimony trioxide has caused a deterioration in the physical properties of the resin, specifically, a reduction in strength and a deterioration in the optical properties of the material. Thus when halogenated retardant compounds are used alone, they generally do not perform satisfactorily in producing a flame retardant material. When inorganic particulates are added, the physical properties of the material, particularly mechanical strength and optical properties, are greatly diminished.